Re: SDL-News: Delays in Channels

Subject: Re: SDL-News: Delays in Channels
Date: Mon Jan 27 1997 - 10:18:05 GMT

The originator of this message is responsible for its content.

-----From Rick Reed TSE <> to sdlnews -----

Sanjay Chakravarty <> wrote:

>My conclusion is that SDL88 cannot be used as a universal modeling

>language. It is confined to less critical systems like

>telecommunications only, right?

Wrong! SDL-88 could be used with non-delaying communication between

processes by removing all the blocks and putting all the processes in one

block so that the processes communicate by (non-delaying) signal routes.

Of course, removing the blocks may make the system difficult to understand,

so it is better to use SDL-92 and non-delaying channels. There are several

other advantages in using SDL-92, such as the type based constructs which

aid the re-use of models.

SDL-88 does not actually REQUIRE the delay to be random in channels. The

model is that there will be some (perhaps not measurable!) time between

signal being put into the channel and it being put into the input queue of

receiving process instance. It is possible (in fact it is likely) that the

delay on a particular channel is (more or less) constant. The language just

does not specify the delay (fixed or random) - just that there is one. A

simulator that allows the delay of each channel to be specified, does not

therefore conflict with SDL-88.

The signals in one channel are always kept in order, as pointed out by

Amardeo Sarma.

There is a good case for additional attributes on delaying channels and

also timing of transitions between states so that performance can be more

accurately modelled. This would produce a "timed SDL", a subject of further

study. Your views would be a useful input to SDL community.

Rick Reed, TSE Limited

13 Weston House, 18-22 Church Street

Lutterworth Leicestershire LE17 4AW United Kingdom

Tel +44 14 55 55 96 55; Fax +44 14 55 55 96 58


P.S. I am please to see sdlnews being used for this discussion.

-----End text from Rick Reed TSE <> to sdlnews -----

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